This invention relates to an apparatus for shooting foundry cores or molds with molding materials, the apparatus comprising a shooting head with an inlet side and an outlet side, a shooting plate associated to the shooting head and containing at least one shooting nozzle, and a clamping head associated to the shooting head on its inlet side and having at least one air supply for a leakproof application of compressed air to the shooting head, the clamping head being movable by means of a cylinder-piston arrangement.
In the foundry practice, core shooting heads have been known for many years. For casting molded products, the foundry cores and molds are molded of core sand separately in most cases, then combined and joined to one another to from a foundry mold. An essential component of the core-shooting machines are the so-called shooting heads with shooting plates accommodating the shooting nozzles. It has been common practice to fill the core sand, i.e. quartz sand compounded or coated with binding agents, into the shooting heads in question, whence it is blown or shot under a very high air pressure through nozzles arranged in the shooting plate into the respective molds.
Known per se from DE-OS 23 04 564 is an apparatus for automatically making molds and cores for use in foundries, in which the molding sand is injected into the shooting head, together with the compressed or shooting air necessary for the shooting, from a vertically rigidly mounted hopper. The compressed air enters via a connection laterally arranged on the shooting head directly into the interior of the shooting head, the connection for the compressed air being provided on the side of the shooting head. As it enters, the compressed air swirls the sand falling into or being already in the shooting head, so that local turbulences occur within the shooting head. After its entry into the shooting head, the compressed air impacts upon the opposite wall of the shooting head, whence it is deflected and redirected toward the sand.
Accordingly, the compressed-air supply occurs in an uncontrolled manner, inasmuch as a controlled, homogeneous biasing of the sand with compressed air is absent within the shooting head. The "compressed-air jets" locally occurring in the known apparatus drill, so to speak, holes into the sand being in the shooting head, or even cause the sand to precompact locally, which in most cases has already been mixed or coated with binding agents. As a result of this inhomogeneous injection of compressed air and premature compacting, it is therefore necessary to increase again the pressure necessary for the shooting.
Thus, as in the above-described apparatus of the prior art, there exists the risk that the molding sand is unintentionally precompacted already in the shooting head, so that substantial pressures are needed for the actual shooting. Moreover, the molding sand already accelerated by the shooting air drops from a considerable height into the shooting head, thereby tending to create an unwanted, premature compacting as a result of its own weight, and causing an uneven distribution of the molding sand in the shooting head.
The apparatus known from practice, or at least in part from DE-OS 23 04 564 is however also problematic, inasmuch as upon completion of the core shooting process, it requires that the clamping head be separated from the shooting head, so as to permit sand to be reloaded via a corresponding hopper device or the like. Upon opening the shooting head or one of the valves associated with the shooting head, the compressed air remaining in the shooting head escapes suddenly therefrom, and entrains to the outside of the shooting head not only suspended particles, but also sand particles, miniature particles and free resins. As a consequence thereof, the surrounding of the apparatus in question is polluted or contaminated on the one hand, and surrounding machine parts are subjected to an increased, abrasive wear by the backflow of particles. Likewise, it is possible that sand particles, as they flow back, enter into the valve area supplying the compressed air, and even into the pump region, and contribute there to wear, or even to damage.
Essential in the known apparatus in question is by all means that as a result of the uncontrolled situation within the shooting head, it has until now been absolutely necessary to shoot under high and, if need be, pulsating air pressures, whereby the sand exiting from the shooting nozzles always impacts upon walls of the mold to be filled and has there an extremely abrasive effect. Stated otherwise, the shooting nozzles operate in the sense of a sand blasting gun, so that the core sand exiting under a high pressure successively damages the mold to be filled or changes it in its geometry. Both particles separated from the mold and split core sand or separated synthetic resins are carried to the outside of the shooting head in a disadvantageous manner, after completion of the core shooting, when the shooting head is opened or ventilated.
A further disadvantage of core shooting under high air pressure can be seen in that the high air pressures cause the core sand to compact in the region of its injection already when it is shot into the mold. As a consequence, a formlocking filling of the mold is precluded, in particular in the case of complicated geometries, or, in the least, substantial gradients of density develop.
Furthermore, the high air pressures and the resultant heavy impact of the sand upon the walls of the particular mold cause a binding agent adhering to the sand to blast off or separate, and last not least a nonuniform distribution of sand and binding agents will occur as a result of differences in the density between the sand and binding agents. Gases which are released at high temperatures from concentrations of binding agents prevent again a uniform compacting or the formation of a flawless core.
Finally, in the conventional core shooting practice a serious problem lies in that the shooting heads are filled beyond the absolutely necessary measure regardless of the volumes of the cores to be shot. Consequently, it is necessary to blast the compressed air required for the shooting, even when the dimensions of the cores to be shot are very small, through the sand deposit in the shooting head, or to accelerate the core sand particles which lie directly against the shooting nozzles. A substantial volume of sand in the shooting head is therefore absolutely necessary, also for the reason that the compressed air flowing into the shooting head in an uncontrolled manner drills, at least in part, holes into the sand, and upon reaching the shooting plate of the nozzles arranged therein, largely prevents an exiting, i.e. a shooting of the core sand. On the one hand, the large dimensions of the shooting heads as are required for shooting large cores, and on the other hand the substantial volume of core sand that needs to be penetrated by the compressed air, however, make it absolutely necessary to apply the high and, if need be, even pulsating pressures which have previously been found to be extremely disadvantageous.
It is therefore the object of this invention to provide an apparatus for shooting foundry cores or molds with molding materials, which allows to apply compressed air at least largely uniformly to the molding materials located in the shooting head.